Undertaking on-site construction of lithium-ion battery industry equipment, plasma cladding coatings, and nano-ceramic coatings.

Guangzhou Sanxin Company utilizes American Miller plasma cladding equipment and technology to perform on-site cladding of nano-ceramic coatings, which are suitable for hopper, screw, and ribbon mixing and conveying systems in the lithium-ion new energy industry.

HVOF Supersonic Flame Process: In supersonic flame spraying, oxygen and aviation kerosene are mixed in a premixing system and then burned in a high-pressure combustion chamber. The resulting flame jet, combined with high-pressure air passing through a Laval nozzle, generates a high-temperature, high-velocity flame stream that heats metal-ceramic powders to a semi-molten state.

[Coating Preparation] Thermal Barrier Coating

1. Introduction to Thermal Barrier Coatings Thermal barrier coatings, also known as thermal insulation or heat-insulating coatings (Thermal Barrier Coatings, abbreviated as TBC or TBCs in English), are coating systems designed to provide effective thermal insulation, oxidation resistance, and corrosion resistance for components. They create a significant temperature drop between the high-temperature combustion gases and the base metal of the component, thereby extending the service life of hot-end components, reducing cooling requirements, and improving the thermal efficiency of thermal machinery. The basic principle behind these coatings is to spray a layer with very low thermal conductivity or thermal diffusivity onto the surface of a metallic substrate. This coating must be able to withstand large temperature gradients when operating in high-temperature thermal environments. Research on TBCs began in the 1940s, and they were first applied to the combustion chambers of JT8D engines in the late 1960s. Later, they were also used in JT9D engines. Ground durability tests on the guide vanes and first- and second-stage turbine blades of the JT9D engine showed that blades equipped with TBCs remained in good condition after 2,778 cycles, whereas blades without TBCs suffered noticeable damage to their trailing edges after just 1,500 cycles. GE in the U.S. has adopted an improved plasma-sprayed TBC, which has extended the total service life of combustion chambers to over 30,000 hours. Typically, TBCs consist of a metallic bond coat and a ceramic top coat. The metallic bond coat primarily serves to firmly bond the ceramic top coat to the substrate metal. The ceramic top coat mainly provides thermal insulation and corrosion resistance, requiring low vapor pressure, low thermal conductivity, low thermal emissivity, high thermal emissivity, and excellent resistance to thermal fatigue or thermal shock. Calculations show that using a 0.25 mm-thick zirconia thermal barrier coating can reduce the substrate metal temperature by about 170°C—a value greater than the cumulative increase in temperature tolerance achieved for blade alloys over the 20-year period from 1965 to 1985 due to continuous human efforts. The application of TBCs has yielded remarkable results: not only have manufacturing costs and specific fuel consumption been reduced, and the demand for cooling air decreased, but blade durability has also been significantly improved. According to reports, applying a 0.25 mm-thick ceramic thermal barrier coating to the first-stage turbine blades of aviation gas-turbine engines reduces cooling air requirements by 6%, improves specific fuel consumption by 13%, and increases blade life by a factor of four. As a result, TBC technology has been widely adopted across various industrial sectors to enhance thermal efficiency—for example, in gas turbines and internal combustion engines. In the U.S., many aircraft engines and nearly all land-based and marine gas turbines—including flame tubes, swirlers, afterburner chambers, shroud plates, fuel nozzles, exhaust ducts, igniter plates, combustion chamber liners, flame stabilizers, and turbine blades—have adopted TBC technology. Approximately several hundred tons of zirconia material are used annually for TBC applications, and the scope of these applications continues to expand. According to research by the Gorham Advanced Materials Institute in the U.S., the proportion of TBC applications in diesel engines will surpass that in the aerospace industry in the future. Moreover, TBC applications in automobiles and motorcycles are also steadily increasing. In Sweden, a single Volvo Aircraft division alone consumed nearly 10 tons of zirconia in 1997, doubling its consumption compared to 1995. With advances in science and technology, numerous fields such as aerospace, aviation, gas power generation, chemical engineering, and metallurgy have driven the research and development of thermal barrier coatings. Today, TBCs are widely used. For instance, tuyeres and slag outlets in blast furnaces, which operate at temperatures ranging from 1,100 to 1,450°C, are subjected to erosion by high-speed pulverized coal and attack by molten iron. Applying TBCs as heat-resistant protective coatings can significantly extend their service life. New atomizing metal nozzles coated with TBCs exhibit excellent corrosion and thermal-shock resistance, have long operational lifetimes, and play a crucial role in ensuring the quality of ultrafine powders. In the automotive industry, valve seats in engine intake and exhaust ports coated with TBCs can reduce component wear. TBCs are also commonly used for piston crown and edge areas made of lightweight aluminum alloy substrates. Some experts predict that in the next decade, TBCs will find even broader applications. Thermal barrier coatings undoubtedly possess great technical potential and promising prospects for development. However, there are still some issues that require further improvement, including controlling coating adhesion, studying coating failure mechanisms, and determining coating performance. Among these, controlling coating adhesion is the most critical issue. Coating adhesion, also known as bonding strength or cohesive strength, is a key quality indicator directly affecting the performance of the coating. Coating spalling is the primary form of component failure and a major factor limiting the wider adoption of thermal barrier coatings in gas-turbine engines. The main causes of coating spalling include oxidation of the bond coat and mismatch in thermal expansion coefficients between the substrate metal and the ceramic coating, resulting in significant strain mismatch. The development of thermal barrier coatings has been a continuous process of improving and addressing these two aspects. 2. Design of Thermal Barrier Coatings The design of thermal barrier coatings involves selecting coating composition, designing coating structure, and choosing appropriate spraying methods. (1) Composition Selection 1. Bond Coat Typical bond coat materials are MCrAlX alloys, where M represents the basic constituent elements of the bond coat, generally belonging to the iron group or high-melting-point metals, or combinations thereof—for example, Ni, Co, Fe, Ni-Co, Ni-Fe, etc. X denotes active metals added to enhance bonding strength and improve the coating’s oxidation resistance, including relatively reactive elements such as Y, Hf, Sc, Ce, La, Th, etc.; among them, Y is the most commonly used. Employing aluminizing processes to form an aluminum-rich layer on the surface of the bond coat can reduce the oxidation rate of the bond coat and extend the service life of the TBC. Adding Re and Ta to CoNiCrAlY can significantly improve the bond coat’s oxidation resistance and mechanical properties. 2. Ceramic Top Coat Currently, the ceramic top coats in TBCs are predominantly fully stabilized or partially stabilized zirconia ceramics. Since pure zirconia crystals undergo different crystal phase transitions with temperature changes, when the temperature exceeds 1,000°C, the monoclinic crystal phase transforms into the tetragonal phase, accompanied by a 7% volume change. During subsequent cooling, the monoclinic structure reverts, but the volume cannot return to its original state—resulting in irreversible volume changes during heating and cooling cycles. Such phase transformations and volume changes generate significant thermal stresses within the coating under thermal cycling conditions, leading to early cracking and even spalling failures. Therefore, stabilizers must be added to pure ZrO2 crystals. After adding stabilizers to pure ZrO2 crystals and undergoing sintering or melting treatment, solid solutions are formed, yielding cubic-stabilized ZrO2 with extremely low thermal expansion coefficients and stable throughout the entire temperature range below the melting point. However, although fully stabilized cubic-phase ZrO2 exhibits predictable expansion and contraction at high temperatures, its linear expansion and contraction rates remain substantial, which is detrimental to enhancing thermal-shock resistance. Thus, partially stabilized zirconia, composed of a mixed structure of monoclinic and cubic phases, is typically used instead. At high temperatures, the monoclinic phase undergoes a volume-reducing transformation, while the cubic phase expands with rising temperature; these two opposing changes mutually suppress each other, giving partially stabilized ZrO2 a lower average thermal expansion coefficient and better thermal-shock resistance than fully stabilized ZrO2. Stabilizers added to zirconia include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), and cerium oxide (CeO). Among these, CaO stabilizers are added at concentrations of 5%, 6%, 8%, 10%, 15%, and 30%. As the CaO content increases, the coating’s hardness also rises. Coatings with up to 30% CaO have exceptionally high hardness and excellent resistance to high-temperature particle erosion. However, CaO-stabilized ZrO2 coatings, if exposed long-term or cyclically to temperatures above 1,093°C, tend to have CaO diffuse out of the stabilized ZrO2 crystal lattice, thus limiting the coating’s usable temperature range. They can only be used continuously at temperatures above 845°C and below 1,093°C; beyond 1,093°C, they can only be used for short periods. MgO stabilizers are typically added at concentrations of 20–30%; at this level, ZrO2 remains structurally stable at various temperatures, especially during high-temperature thermal cycling. MgO-stabilized ZrO2, below 1,400°C, maintains a balanced microstructure consisting of either the tetragonal or monoclinic phase plus MgO. During thermal cycling, MgO precipitates from the solid solution, increasing the coating’s thermal conductivity and reducing its insulating ability, thus limiting its widespread use. On the other hand, Y2O3-partially stabilized ZrO2, when used continuously at temperatures up to 1,650°C, does not exhibit the same tendency for CaO-like diffusion outside the crystal lattice as CaO-stabilized ZrO2 or MgO-stabilized ZrO2. It boasts superior chemical and thermal stability and is therefore an outstanding thermal barrier coating material with the highest usable temperature. Its addition levels are 6–8%, 13%, and 20%; the first two represent partially stabilized ZrO2, while the last one is fully stabilized ZrO2. For thermal barrier coatings, partially stabilized zirconia offers better thermal-shock resistance, making 6–8% yttria-partially stabilized zirconia the preferred material for ceramic top coats. In recent years, studies on partially stabilized additives such as Y2O3, Nd2O3, and Sc2O3 (PSZ) have revealed that under rapid cooling conditions, the ZrO2 ceramic layer contains partially or fully “non-transformed” tetragonal phase t′. Although still metastable, this phase does not decompose into equilibrium tetragonal and cubic phases under high-temperature cycling conditions between 1,100 and 1,200°C. In contrast, 6–8% Y2O3-ZrO2 (YSZ) coatings maintain the t′ phase without decomposition at 1,100–1,200°C. In CeO-Y2O3-ZrO2, the t′ phase is more stable than in 8% YSZ, but it shows poorer resistance to corrosive media containing V, S, and other elements. Meanwhile, Sc2O3-Y2O3-ZrO2 (SYSZ) exhibits higher t′ phase stability and better resistance to hot salt corrosion at high temperatures (1,400°C). (2) Coating Structure Design Thermal barrier coating structures mainly fall into three categories: double-layer, multi-layer, and gradient structures. The double-layer structure consists of a ceramic top coat (mostly ZrO2-based ceramic) sprayed onto a high-temperature alloy substrate and a bond coat (typically MCrAlY-type). The ceramic top coat primarily provides thermal insulation and oxidation resistance, while the bond coat enhances the adhesion between the ceramic top coat and the substrate, improves thermal expansion coefficient matching tolerances, and boosts oxidation resistance. Due to its simple structure and ease of implementation, the double-layer thermal barrier coating is currently the most widely used type of TBC.The multi-layer structure is primarily designed to reduce thermal expansion mismatch between the ceramic top layer and the metallic bond coat by introducing an intermediate layer between them. Alternatively, to further enhance the oxidation resistance of the thermal barrier coating, a thin Al2O3 layer can be added between the ceramic top layer and the metallic bond coat. However, the addition of this Al2O3 layer provides only marginal improvement in thermal shock resistance, and the process is complex, resulting in slightly poorer coating repeatability and reliability. A gradient-structure thermal barrier coating refers to a coating in which the chemical composition, microstructural features, and mechanical properties gradually vary continuously along the thickness direction—from the metallic bond coat to the ceramic top layer. This structure improves both the bonding strength between the coating and the substrate and the cohesive strength within the coating itself, delivering high-temperature performance that is ideal for coating design and exhibiting superior thermal shock resistance compared to bilayer coatings. However, in practical preparation, what is typically obtained is a multilayer stepped structure, and the preparation technology remains complex, placing it still at the laboratory research and development stage. (3) Selection of spraying methods. Due to the high melting point (2760℃) and low thermal conductivity (approximately 1.0–2.0 W/mK) of ZrO2 ceramic materials, among the thermal spraying processes described in Chapter 2, only arc spraying, cold gas dynamic spraying, high-velocity flame spraying, oxy-acetylene flame remelting, medium-frequency induction remelting, and plasma spray welding cannot be used for preparing ZrO2 ceramic coatings. All other thermal spraying processes are suitable for this purpose. However, as requirements for coating performance continue to rise, plasma spraying has become the primary method for fabricating thermal barrier coatings. In practical applications, though, due to limitations in conditions or to reduce costs while maintaining performance, various thermal spraying processes are often employed. Based on whether a single device or multiple devices are used in the preparation of thermal barrier coatings, the fabrication processes can be categorized into single-process and composite-process techniques. The single-process technique involves using the same spraying method for both the metallic bond coat and the ZrO2 ceramic top layer, including atmospheric plasma spraying, low-pressure plasma spraying, vacuum plasma spraying, explosion spraying, and high-velocity plasma spraying. The composite-process technique involves using different spraying methods for the metallic bond coat and the ZrO2 ceramic top layer, including: ① a vacuum-plus-atmospheric plasma composite spraying process, where the metallic bond coat is prepared using vacuum plasma spraying and the ZrO2 ceramic top layer is prepared using atmospheric plasma spraying; ② a high-velocity flame-plus-atmospheric plasma composite spraying process, where the metallic bond coat is prepared using high-velocity flame spraying and the ZrO2 ceramic top layer is prepared using atmospheric plasma spraying; ③ a high-velocity flame-plus-high-velocity plasma composite spraying process, where the metallic bond coat is prepared using high-velocity flame spraying and the ZrO2 ceramic top layer is prepared using high-velocity plasma spraying. To address the issues of high porosity and cracks in plasma-sprayed TBCs, which lead to reduced oxidation resistance and shorter coating life, extensive application exploration and research have been conducted both domestically and internationally in two distinct areas: laser surface remelting and laser cladding for TBC preparation. There are two main laser-based TBC fabrication processes: the single-pass laser cladding method and the double-pass laser cladding method. The single-pass laser cladding method for TBC preparation is a relatively new field, with research reports emerging only in the past decade. It mainly includes two approaches: the pre-placement method and the powder-feeding method. In the pre-placement method, a partially stabilized YPSZ powder mixed with Ni-based composite powder is pre-placed onto the substrate, then subjected to CO2 laser cladding to obtain a layered composite coating. The surface consists of a dense ZrO2 ceramic layer, beneath which lies a Ni-based alloy transition layer. The upper part of the ZrO2 ceramic layer exhibits equiaxed crystals, while the middle and lower parts show columnar crystals predominantly composed of the t′ phase. In the powder-feeding method, a feeding device delivers a mixture of partially stabilized YPSZ and alloy composite powder into the laser irradiation zone, where the laser melts and fuses the material onto the substrate, producing an automatically layered ceramic layer characterized by columnar crystal structures, mostly composed of the t′ phase. The double-pass laser cladding method involves first applying a ZrO2 ceramic layer onto the substrate surface via plasma spraying, followed by laser remelting treatment. This process yields a ceramic overlay with a smooth, continuous, dense surface free from defects such as cracks and pores, thereby avoiding the crack problems that cannot be solved by the powder-feeding laser cladding method. The microstructure of the ceramic overlay produced by the double-pass laser cladding method consists of columnar crystals whose growth direction is perpendicular to the substrate. The double-pass laser cladding method offers a feasible approach for preparing high-performance, low-cost TBCs, but it is still in the preliminary research stage. High-temperature performance testing remains incomplete, and further in-depth studies are needed to clarify the effects of cladding process parameters, layered microstructure, composition, morphology, internal and external quality, and high-temperature performance on the coating’s service life. In recent years, thermal barrier coatings prepared by electron-beam physical vapor deposition (EB-PVD) have attracted attention due to their excellent thermal shock resistance. Research on EB-PVD thermal barrier coatings began in the 1970s, with breakthroughs achieved by Pratt & Whitney in the United States in the 1980s. Subsequently, this technology was successfully applied in countries such as Germany. EB-PVD thermal barrier coatings are fabricated using a high-energy electron beam.

We specialize in thermal spray coating services for various industries.

If your products have high requirements for surface finish and dimensional accuracy, or if they will be in long-term contact with liquids and thus demand enhanced wear resistance and corrosion protection, you should choose our company’s tungsten carbide coating applied using the American Praxair JP8000 equipment. From materials to equipment, processes to solutions—we’ve got it all covered in coatings.

Tungsten Carbide Spraying and Processing

In the new-energy lithium-battery industry, various types of equipment—such as screw shafts, screw conveyors, battery raw-material crushers, mixers, conical hoppers, powder feeders, and feeding machines—are coated with wear-resistant tungsten carbide coatings on their surfaces.

Turbine blade coating equipment / Gas-supersonic thermal spraying equipment

Supersonic Spray Equipment, Tungsten Carbide Coating, HVOF Spray Equipment

Roller-sprayed tungsten carbide coating—supersonic spraying for wear and corrosion resistance

Characteristics of Tungsten Carbide Thermal Spray Coatings: 1. The flame jet velocity is extremely high—typically 53 times the speed of sound. 2. The coating is highly dense with strong bonding strength; its porosity can be less than 1%, and the bonding strength can exceed 70 MPa. 3. The coating material exhibits low oxidation, minimal carbon loss, and high hardness.

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